1. Field of the Disclosure
The present invention is generally related to photodiodes, and more specifically, the present invention is directed to photodiodes utilized in photon sensors.
2. Background
An image capture device includes an image sensor and an imaging lens. The imaging lens focuses light onto the image sensor to form an image, and the image sensor converts the light into electric signals. The electric signals are output from the image capture device to other components of a host electronic system. The electronic system may be, for example, a mobile phone, a computer, a digital camera or a medical device.
There is a continuing demand to reduce the size of image sensors, which results in the smaller pixel cells for an image sensor with the same resolution. One type of photodetector that may be used in an image sensor or in a light detector is a single photon avalanche diode (SPAD). A SPAD normally needs a guard ring or isolation to overcome the problem of premature edge breakdown and interference between adjacent pixels. Known designs to create the guard ring or isolation increase the area of each pixel cell and sacrifices fill factor. Furthermore, as image sensors are miniaturized, the pixel cells contained therein suffer from increased dark current rates.
Corresponding reference characters indicate corresponding components throughout the several views of the drawings. Skilled artisans will appreciate that elements in the figures are illustrated for simplicity and clarity and have not necessarily been drawn to scale. For example, the dimensions of some of the elements in the figures may be exaggerated relative to other elements to help to improve understanding of various embodiments of the present invention. Also, common but well-understood elements that are useful or necessary in a commercially feasible embodiment are often not depicted in order to facilitate a less obstructed view of these various embodiments of the present invention.